Petrology and geochemistry of the Saddle North Cu-Au porphyry deposit, British Columbia, Canada.

Abstract

The Saddle North porphyry Cu-Au deposit, northwestern British Columbia, Canada, is located in the Upper Triassic Stuhini Group and is associated with the Late Triassic to Early Jurassic Tatogga Suite intrusions. This study integrates petrographic, geochemical, and geochronological data to characterize the deposit's intrusive evolution, alteration assemblages, and mineralization processes. Four intrusive phases (FQMP-I1 to FQMP-I4) of feldspar–quartz–monzodiorite porphyry were identified based on petrographic and geochemical criteria, demonstrating a progressive compositional evolution and varying intensities of potassic alteration. High-precision LA-ICP-MS U–Pb zircon geochronology yielded crystallization ages ranging from 205.3 ± 1.7 Ma to 208.2 ± 1.8 Ma, confirming the temporal overlap between intrusive emplacement and hydrothermal activity. Re-Os dating of molybdenite veins returned a model age of 205.6 ± 0.8 Ma, corroborating a genetic link between mineralization and magmatism. Whole-rock geochemistry reveals that the intrusions are alkaline to weakly calc-alkaline, with moderate to strong Nb, Ti, and Eu depletions consistent with subduction-related arc magmas. Micro-XRF maps further constrain the spatial distribution of key alteration minerals and elemental enrichments within the core of the deposit. Eight vein types were recognized and categorized into four paragenetic stages: early (A–D), main (C, F, G), late (E, F, G), and post-mineral (G, H). Early-stage veins (A- and B-type) are associated with magnetite, chalcopyrite, and molybdenite and are found in potassic-altered FQMP-I1 and I2 intrusions. The vein paragenesis and alteration zoning indicate a progressive decline in temperature and fluid metal content during hydrothermal evolution. These findings collectively support a magmatic-hydrothermal continuum model for Saddle North, similar to other porphyry systems in the Golden Triangle, such as Red Chris and Galore Creek, emphasizing its potential as a significant Cu-Au mineralizing centre in the Canadian Cordillera.